KEVOS® MAKEOS · Mechanics
Machine Foundation Block Sizing
How big a concrete block does this machine need, will the soil carry it, and is the block clear of resonance?
Preliminary sizing of a concrete inertia block for a machine: block mass as a multiple of machine mass, depth for the plan area, soil bearing pressure against the allowable, vertical stiffness from the soil’s subgrade modulus, natural frequency of the machine and block on the soil, and the ratio of running frequency to natural frequency against the resonance band.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Machine mass | kg | Mass of the machine on the block. |
| Block mass ÷ machine mass | Block mass as a multiple of machine mass (often 2–3 for rotating machines, 3–5 or more for reciprocating and impact machines). | |
| Concrete density | kg/m³ | Density of reinforced concrete. |
| Block length | m | Plan length of the block. |
| Block width | m | Plan width of the block. |
| Allowable soil bearing pressure | kPa | Allowable bearing pressure of the soil (from a geotechnical report). |
| Soil subgrade modulus (vertical) | MN/m³ | Vertical modulus of subgrade reaction for the soil (from the geotechnical report). |
| Lowest running speed | rpm | Lowest steady running speed producing vibration. |
Method and formulas
- Block mass = ratio × machine mass; depth = mass ÷ (density × length × width).
- Bearing pressure = (machine + block) g ÷ plan area.
- Vertical stiffness k = subgrade modulus × plan area; natural frequency f_n = √(k ÷ m_total) ÷ 2π.
- Frequency ratio r = running frequency ÷ f_n; keep clear of 0.5 < r < 1.5.
- Example: a 5000 kg machine needs a 1.0417 m deep block, bearing 32.689 kPa on the soil.
Limitations
- Preliminary rule-of-thumb sizing; rocking modes, embedment and dynamic loads need a foundation design by a structural engineer.
- Subgrade modulus depends on footing size and soil; use project data.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a foundation block for a press, compressor or generator
- Check soil bearing before pouring
- Avoid a foundation that resonates at running speed
Who it is for
- Plant engineers
- Civil and structural engineers
- Installation engineers
What you get
- Block mass, volume and depth
- Soil bearing pressure
- Natural frequency and frequency ratio
Interpreting the result
- A block running well above its natural frequency (r > 1.5) isolates best; well below (r < 0.5) is stiff and also acceptable.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3237–3238, 197–198. Topic reference; no source tables or recommended settings are reproduced.
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